'Sarahsaurus' discovery shows opportunistic nature of dinosaurs

Robert Reisz, biology professor at University of Toronto, Mississauga. He's the Canadian scientist involved in the discovery of Sarahsaurus, a new dinosaur that is forcing a rethink of the evolution and distrubution of the species about 200 million years ago.

Photograph by: University of Toronto
, Photo Handout

The discovery of a new dinosaur species by a Canadian scientist and two U.S. colleagues is forcing a major rethink about the early evolution of the species, suggesting the giant reptiles were less competitive with rivals and more opportunistic in their northward migrations as they spread to North America some 200 million years ago.

Robert Reisz, a biology professor at the University of Toronto's Mississauga, Ont., campus, has co-authored a paper about the discovery with University of Texas paleontologist Tim Rowe and Hans-Dieter Sues, curator of vertebrate paleontology at the National Museum of Natural History in Washington, D.C.

Reisz and Sues were documenting fossils found in Arizona when they learned that Rowe was studying a separate site in the state with remains from the same, previously unknown species — a long-necked plant eater the team has called sarahsaurus.

Rowe's research had been stymied because the bones he collected didn't include anything from the specimen's head. Remarkably, the fossils Reisz and Sues were studying included a sarahsaurus skull.

The combined remains revealed a creature about 4.3 metres long and weighing about 110 kilograms. Sarahsaurus is classified as a small, early member of the sauropod group of dinosaurs that evolved to include the largest land animals in Earth history. They include the 50-metre-long, 120-tonne giant of all dinosaurs, Amphicoelias fragillimus, known only from a single and subsequently lost bone from a Colorado fossil bed.

The sarahsaurus discovery, detailed in the latest edition of the Proceedings of the Royal Society B, combines with other finds of related dinosaur remains to show that the animals moved from their original southerly habitats into the future North America in "several separate dispersal events" rather than in the "sweepstake" style rush of an unstoppable competitor, Reisz told Postmedia News.

"Until recently, we've viewed dinosaurs as very successful animals that outcompeted other species wherever they went," Reisz stated in a summary of the team's findings. "But this study puts dinosaurs in a very different light — that they were more opportunistic creatures that moved into North America only when a mass extinction event made eco-space available to them."

Scientists have long known that a massive die-off of species occurred about 200 million years ago, at the end of the Triassic era. The new study suggests that the entry of sarahsaurus and its fellow sauropods into North America occurred in three distinct waves and only after the extinction event, when habitats were relatively free to occupy.

"They didn't invade the neighbourhood," Rowe said in separate statement released by the University of Texas. "They waited for the residents to leave and when no one was watching, they moved in."

The new species was named for a Texas-based benefactor of dinosaur research and education, Sarah Butler. Rowe said sarahsaurus has not only shed fresh light on dinosaur migration and evolution, but has also sparked a mystery related to the development of its powerful front feet and claws.

"We've never found anything like this in western North America," Rowe said.

"Its hand is smaller than my hand, but if you line the base of the thumbs up, this small hand is much more powerfully built than my hand and it has these big claws. It's a very strange animal. It's doing something with its hands that involved great strength and power, but we don't know what."

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Robert Reisz, biology professor at University of Toronto, Mississauga. He's the Canadian scientist involved in the discovery of Sarahsaurus, a new dinosaur that is forcing a rethink of the evolution and distrubution of the species about 200 million years ago.

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